1. Field of the Invention
The present invention relates to a capacitive device utilizing an electric double layer and containing a solid electrolyte therein.
2. Description of the Prior Art
Carbon or silver chalcogenide such as Ag.sub.2 Se-Ag.sub.3 PO.sub.4 has been employed as a polarizable electrode in conventional solid state capacitors utilizing electric double layers formed at an interface between a polarization electrode and a solid electrolyte. Non-polarizable Ag has been employed as a counter electrode, and a solid electrolyte of Ag ionic conductivity such as RbAg.sub.4 I.sub.5, NR.sub.4 Ag.sub.4 I.sub.5, Ag.sub.3 SI and Ag.sub.6 I.sub.4 WO.sub.4 as the solid electrolyte, respectively. The solid state capacitor of such a type has an advantage that its capacity is large in comparison with a solid state device using a space charge effect, a capacitive device using a dielectric, or an IC device where charges at the semiconductor surface are used for capacitive elements. However, such conventional solid state capacitors have a shortcoming that they are very expensive owing to expensive materials such as silver and silver salt.
The present inventors have developed capacitive devices wherein a molded compound obtained by mixing Cu.sub.x S(x.ltoreq.2) and a solid electrolyte was employed for a polarizable electrode, a counter electrode and a reference electrode, and the devices are filled with a solid electrolyte of Cu.sup.+ ionic conductivity produced from a reactant of cuprous halide and N-methylhexamethylenetetramine halide or N,N'-methyl-triethylenediamine halide. Such capacitive devices were devised for the sake of cost reduction by employing Cu.sub.2 S and the solid electrolyte of Cu.sup.+ ionic conductivity without using Ag as a counter electrode material. They are free from breakdown at an early stage liable to take place in a capacitive device where Ag as the counter electrode material is simply replaced with Cu. However, the capacitive devices have turned out to be not satisfactory, since they have the following shortcomings. At room temperature the solid electrolyte shows low ionic conductivity of 10.sup.-2 /cm which is 1/5 to 1/10 of the ionic conductivity of a silver salt, thus only small quantity of current can flow comparing to the silver salt. Further, cuprous halide is again deposited in the solid electrolyte and thus a leak current flows through the deposited compound (in other words, ionic conduction does not play a primal role at this stage). Accordingly, charge storage capability is worse than that of the conventional capacitive devices containing silver salt.